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Description

The genus Ilex is widespread throughout the temperate and subtropical regions of the world. It includes species of trees, shrubs, and climbers, with evergreen or deciduous foliage and inconspicuous flowers. Its range was more extended in the Tertiary period and many species are adapted to laurel forest habitat. It occurs from sea level to more than 2,000 metres (6,600 ft) with high mountain species. It is a genus of small, evergreentrees with smooth, glabrous, or pubescent branchlets. The plants are generally slow-growing with some species growing to 25 m (82 ft) tall. The type species is the European holly Ilex aquifolium described by Linnaeus,[2]

Plants in this genus have simple, alternate glossy leaves, typically with a spiny toothed, or serrated leaf margin. The inconspicuous flower is greenish white, with four petals. They are generally dioecious, with male and female flowers on different plants, although there are exceptions.

The small fruits of Ilex, although often referred to as berries, are technically drupes.[3] They range in color from red to brown to black, and rarely green or yellow. The "bones" contain up to ten seeds each. Some species produce fruits parthenogenetically, such as the cultivar 'Nellie R. Stevens'. The fruits ripen in winter and thus provide winter colour contrast between the bright red of the fruits and the glossy green evergreen leaves. Hence the cut branches, especially of I. aquifolium, are widely used in Christmas decoration. The fruits are generally slightly toxic to humans, and can cause vomiting and diarrhea when ingested. However, they are a very important food source for birds and other wildlife.

Etymology

Ilex in Latin means the holm-oak or evergreen oak (Quercus ilex). Despite the Linnaean classification of Ilex as holly, as late as the 19th century in Britain, the term Ilex was still being applied to the oak as well as the holly - possibly due to the superficial similarity of the leaves.[4][5] The name "holly" in common speech refers to Ilex aquifolium, specifically stems with berries used in Christmas decoration. By extension, "holly" is also applied to the whole genus. The origin of the word "holly" is considered a reduced form of Old Englishhole(ġ)n,[6] Middle English Holin, later Hollen.[7][8] The French word for holly, houx, derives from the Old Low Franconian*hulis (Middle Dutch huls).[9] Both are related to Old High Germanhulis, huls,[10] as do Low German/Low Franconian terms like Hülse or hulst. These Germanic words appear to be related to words for holly in Celtic languages, such as Welshcelyn, Bretonkelen(n) and Irishcuileann. [11]

Several romance languages use the Latin word acrifolium (turned into aquifolium in modern time), so Italian agrifoglio, Occitangrefuèlh, etc. [12]

The phylogeography of this group provides examples of various speciation mechanisms at work. In this scenario ancestors of this group became isolated from the remaining Ilex when the Earth mass broke away from Gondwana and Laurasia about 82 million years ago, resulting in a physical separation of the groups and beginning a process of change to adapt to new conditions. This mechanism is called allopatric speciation. Over time survivor species of the holly genus adapted to different ecological niches. This led to reproductive isolation, an example of ecological speciation. In the Pliocene, around five million years ago, the formation of the new orogeny[clarification needed] diversified the landscape and provided new opportunities for speciation within the genus.

The fossil record indicates that the Ilex lineage was already widespread prior to the end of the Cretaceous period. Based on the molecular clock the common ancestor of most of the extant species probably appeared during the Eocene, about 50 million years ago, suggesting that older representatives of the genus belong to now extinct branches.[13] The laurel forest covered great areas of the Earth during the Paleogene, when the genus was more prosperous. This type of forest extended during the Neogene, more than 20 million years ago. Most of the last remaining temperate evergreen forests are believed to have disappeared about 10,000 years ago at the end of the Pleistocene. Many of the then existing species with the strictest ecological requirements became extinct because they could not cross the barriers imposed by the geography, but others found refuge as a species relict in coastal enclaves, archipelagos, and coastal mountains sufficiently far from the extreme cold and aridity and protected by the oceanic influence.

The genus includes about 400 to 600 species, divided into three subgenera:

Range

The genus is distributed throughout the world's different climates. Most species make their home in the tropics and subtropics, with a worldwide distribution in temperate zones. The greatest diversity of species is found in the Americas and in Southeast Asia.

Ecology

Often the tropical species are especially threatened by habitat destruction and overexploitation. At least two species of Ilex have become extinct recently, and many others are barely surviving.[18] The fruits are toxic to humans, though their poisonous properties are overstated and fatalities are almost unknown. [19][20] They are extremely important food for numerous species of birds, and also are eaten by other wild animals. In the autumn and early winter the fruits are hard and apparently unpalatable. After being frozen or frosted several times, the fruits soften, and become milder in taste. During winter storms, birds often take refuge in hollies, which provide shelter, protection from predators (by the spiny leaves), and food. The flowers are sometimes eaten by the larva of the Double-striped Pugmoth (Gymnoscelis rufifasciata). Other Lepidoptera whose larvae feed on holly include Bucculatrix ilecella, which feeds exclusively on hollies, and The Engrailed (Ectropis crepuscularia).

Toxicity

A 'Highclere' holly variety

The berries of various species contain Theobromine, a compound similar to caffeine. In very small doses, theobromine and other caffeines only mildly stimulate the nervous system. However larger amounts can cause dizziness, stomach pain, nausea, diarrhoea, elevated pulse rate, and low blood pressure, as well as drowsiness. [21]

Berries attract birds that eat them after the frosts have reduced toxicity. However, if household pets ingest Holly, they are very liable to be poisoned, and it is a very good idea to keep holly decorations out of reach of pets and/or children.[22]

Cultivation

Many of the holly species are widely used as ornamental plants in gardens and parks, notably:-

Between the thirteenth and eighteenth centuries, before the introduction of turnips, holly was cultivated for use as winter fodder for cattle and sheep.[28] Less spiny varieties of holly were preferred, and in practice the leaves growing near the top of the tree have far fewer spines making them more suitable for fodder.

Culture

Holly - more specifically the European holly, Ilex aquifolium - is commonly referenced at Christmas time. In many western cultures, holly is a traditional Christmas decoration, used especially in wreaths and illustrations, for instance on Christmas cards. Since medieval times the plant has carried a Christian symbolism, as expressed in the well-known carol "The Holly and the Ivy". However, the association of holly with winter celebrations almost certainly pre-dates Christianity. Druids wore holly wreaths on their heads.